1. Field of the Invention
This invention relates to the preparing of structures for etch patterning. More specifically, the invention relates to a planarization process for preparing thin film structures for etch patterning to form the air-bearing surface of a slider for use in a hard drive assembly.
2. Description of Related Art
Conventional magnetic disk drives are information storage devices that utilize at least one rotatable magnetic media disk with concentric data tracks. Read/write transducers are used for performing reading and writing functions on the various data tracks, and storage densities can be improved by utilizing separate transducers such as magnetoresistive and giant magnetoresistive heads. Transducers are typically mounted on the underside of an air bearing slider, which flies relative to the rotating media disk, slightly above the data track. A suspension assembly is used for resiliently holding the slider over the data tracks, and a positioning actuator connected to the suspension moves the transducer across the media to a desired data track and maintains transducer position during a read or a write operation.
A limiting factor in the recording density of a magnetic disk drive is the distance between the transducer and the magnetic media. One goal of air bearing slider design is to “fly” a slider as closely as possible to the magnetic medium without making physical contact with the medium. Smaller spacings, or “fly heights,” are desired so that the transducer can distinguish between the magnetic fields emanating from closely spaced data regions on the disk.
In addition to achieving the smallest possible spacing between the media and transducer, it is also critical that a slider maintain this constant spacing over time. The range of conditions that transducers experience during the normal operation of a disk drive can cause great variations in fly height constancy. When fly heights are not constant, data transfer between the transducer and recording medium may be adversely affected.
Physical features on the air bearing surface (“ABS”) portion of a slider, as well as the manufacturing methods and fabrication materials used, in large part define the slider fly height. The utilization of batch manufacturing processes often introduces variations in the physical characteristics of resultant sliders, which in turn will cause fly height variations in the hard disk assembly. If these variations are too large, nominal slider fly heights must be increased in order to compensate.
In the past, the processes for defining ABS's included using a dry-film resist as the etch mask for a single etch step. Most current air-bearing surface features, however, are formed using two or more etch steps to improve fly height and better fly height control. Moreover, slider air-bearing designs for lower fly height may include small pads or other features that are difficult to pattern using dry film resists. Liquid resists have much better resolution capabilities and have been preferred for forming small air-bearing design features and lowering overall etch step heights.
Current slider manufacture methods utilize strips of slider material which are positioned in rows on a carrier with the ABS side exposed upwards to allow for the eventual patterning of the ABS. After the ABS's are formed the strips of slider materials are diced into separated individual sliders. The liquid resists are typically applied by spin coating groups of sliders at a time. In order to spin coat the liquid resist, the group of sliders must be substantially coplanar, with step heights of less than 5 μm between the sliders. Uniformity in the thickness of resist coatings during the etching process is achieved by minimizing these step heights.
In processing multiple etch designs, ion milling or reactive ion etching (RIE) processes are sometimes used for each etch step. If certain slider row spacings exist, the ion milling etch process results in the formation of redeposited materials on the sides of the rows which cannot be removed. In addition, both ion milling and RIE yield shallow wall profiles which make slider inspection difficult and also affect slider flight characteristics.
Reducing step heights between the air bearing side of sliders for etch patterning is a process generally referred to as planarization. Some planarization processes involve filling in the gaps of sliders on the carriers with a polymeric material, which not only reduces the step height between the slider rows, but also prevents redeposit of etched materials in the gaps.
U.S. Pat. No. 5,516,430 to Hussinger provides a planarization procedure that uses alignment fixtures to accommodate liquid resist applications. A filled thermoplastic material is placed on the rows with a substrate on top. The structure is heated to 400-500° F., causing the encapsulating material (or encapsulant) to melt and flow into the gaps between the rows. The heating process is controlled by maintaining the alignment fixture near ambient temperature to prevent sticking between the encapsulant and fixture. Sufficient heat is applied to melt the material near the air-bearing surface, which may contain thermally sensitive transducers. One problem with this process is the potential seepage of encapsulant onto the air-bearing surface of the slider, which causes photoresist adhesion and imaging problems.
U.S. Pat. No. 5,932,113 to Kurdi, et al. (hereinafter referred to as the “Kurdi patent”) provides a process for preparing an air-bearing slider that uses an adhesive film and an acrylic encapsulating fluid to fill the recesses between the rows during etching. According to the Kurdi patent, the thin films to be etched are applied to a carrier, each of the thin films separated by a recess. Each of the thin films may comprise a transducer-laden ABS. An adhesive film is then generally applied to the ABS side of the thin films. A fluid is then deposited in the recess and held in place by the adhesive film. The fluid may then be cured and the adhesive film removed to provide a planar surface. The ABS side of the row may then be patterned for use by appropriately using an etch mask coating and developing process.
Both Kurdi and Hussigner processes involve the use of an acrylate encapsulant due to the fact that multiple photo/etch steps are necessary to achieve planarization. To enable multiple photo/etch steps, the material used to fill the gaps of sliders must be able to resist process solvents such as propylene-glycol-methyl-ether-acetate or NMP (N-methyl-pyrrolidone) types of solvent during photo/strip. At the same time, these encapsulants must be removed during debonding with NMP. The encapsulant used to fill the gap typically starts out in liquid form, such as acrylate, and becomes cross-linked once it fills the gap of sliders. The cross-linked acrylate can generally withstand the multiple solvent exposures during photo/strip. The cured encapsulant is difficult to remove however because it is insoluble in organic solvents due to the cross-linking, and it bonds well to the slider substrate (e.g., Si/N-58 ceramic). During debonding, an additional process must be employed to mechanically shear off the cross-linked acrylate prior to chemical debonding. This mechanical debonding process causes chips, cracks, and heavy contamination.
Another problem with these prior art processes is incomplete planarization. Encapsulant is introduced into the recesses or gaps between slider rows by capillary action. Blockage of the gaps due to bonding tape or impurities will give rise to incomplete planarization. The same problem results from bubbles in the encapsulating fluid. Another problem is the inability to easily remove all of the encapsulant during the debond process.
Further, the current planarization processes are designed for row level processing, and would be extremely difficult to apply to the etching of ABS directly on an array of individual sliders. For example, the existing mechanical shear debonding processes of cross-linked acrylate encapsulant are neither practical nor feasible for an array of individual sliders, which would require debonding of each slider separately.
Consequently, there is a continuing need for planarization processes that will overcome drawbacks in the prior art, provide increased yields and ease of manufacturability, and which can enable the etch processing of an array of individual thin film elements such as sliders.